Displays

Since 2010 we have established cave drip water hydrological monitoring networks in four contrasting climate zones (Mediterranean, montane, semi-arid and sub-tropical) across continental Australia. Deploying over one hundred automated drip loggers, we combine these long-term monitoring datasets with climate and water isotope data, lidar mapping, electrical resistivity imaging and karst hydrological modelling to provide insights into recharge processes and the impact of hydrological variability on speleothem proxy archives.

We identify increases in drip discharge and compare the timing of those events to antecedent climate conditions (rainfall, evapotranspiration). We find rainfall recharge thresholds vary with climate. At our montane site, recharge occurs after 13 to 31 mm rainfall events, depending on antecedent conditions. At the semi-arid site, recharge occurs after 40 mm rainfall events, and at our sub-tropical sites, recharge occurs following all instances where > 93 mm / week of precipitation occurs, with lower precipitation thresholds (down to 33 mm / week) possible depending on antecedent conditions and at sites with limited vegetation cover. We use these recharge thresholds to constrain simple soil moisture balance models to better understand soil and karst storage volumes. Combined with electrical resistivity imaging, we can relate recharge to the caves to subsurface water flow paths and karst water stores.

At our montane and Mediterranean climate sites, relatively consistent drip water isotopic composition confirms the presence of well-mixed water stores. This allows us to quantify the extent of speleothem oxygen isotope variability due to fractionation associated with changes in drip rate. We identify significant differences in long-term mean drip rates between different drip sites within a cave, and significant differences in event-based drip rate responses within a cave. Drip hydrological variability helps explain the within-cave variability of speleothem oxygen isotope composition observed at both sites, and helps identify the primary drip water oxygen isotope signal.

At our semi-arid site, drip water isotopic composition is dominated by epikarst evaporation and our drip water monitoring demonstrates that recharge events are infrequent (~1.6 per year). Using both observational and modelling data, we quantify the relative importance of evaporative fractionation in the epikarst and fractionation during calcite precipitation. Using modern speleothem samples, we demonstrate that the oxygen isotope signal in this water limited environment reflects the balance between the oxygen isotope composition of recharge and its subsequent fractionation in the soil, epikarst and cave.

How to cite: Baker, A., Treble, P., Hartmann, A., Cuthbert, M., Markowska, M., Berthelin, R., Tadros, C., Leopold, M., and Hankin, S.: Insights into recharge processes and speleothem proxy archives from long-term monitoring networks of cave drip water hydrology , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1686, https://doi.org/10.5194/egusphere-egu2020-1686, 2020.

Mainland Southeast Asia is located on the route of moisture transport of the Indian summer monsoon where hydroclimate records from speleothems have rarely been investigated. Here we present a new multi-proxy data set (δ¹⁸O, δ¹³C, trace elements and grayscale values) of stalagmite KPC1 from Khao Prae cave in western Thailand spanning from approximately 500 CE to 1900 CE. Our multi-proxy data reveal high variability between wet and dry periods during 500-850 CE and 1150-1350 CE, a stable condition between 850-1150 CE, and an overall trend towards dry conditions since 1350 CE. The δ¹³C, trace elements and grayscale values suggest centennial-scale fluctuations driven by local hydrological process at the cave site. In contrast, variations in stalagmite δ¹⁸O reflect integrated changes in rainfall amount from the Indian summer monsoon, supported by two-year monitoring rainfall data. In comparison with other Asian Monsoon records for the last millennia, the KPC1 record shows similarity with speleothem δ¹⁸O records from India, as well as lakes and tree-ring data from mainland Southeast Asia but diverges from records from equatorial regions and the western Pacific. We conclude that hydroclimate variability in the western side of Mainland Southeast Asia is mainly driven by changes in moisture transport from the Indian summer monsoon and modulated by expansion and contraction of the Intertropical convergent zone (ITCZ). However, Pacific Walker circulation (PWC) may have been the overriding control on precipitation on the eastern sides of Mainland Southeast Asia located closely to the western Pacific.

How to cite: chawchai, S., Liu, G., Bissen, R., Scholz, D., Riechelmann, D. F. C., Vonhof, H., Mertz-Krause, R., Tan, L., Chiang, H.-W., and Wang, X.: Hydroclimate variability of western Thailand during the last 1400 years , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-895, https://doi.org/10.5194/egusphere-egu2020-895, 2020.

Western Mediterranean speleothem palaeoclimate records covering the entire Last Glacial period are extremely rare and discontinuous, because the progressive aridity and temperature decrease inhibited continuous carbonate deposition (Budsky et al., 2019; Perez-Mejias et al., 2019). This lack of high-resolution archives impedes a better understanding of key issues regarding the Late Quaternary, such as: 1) The spatio-temporal teleconnection between the northern latitudes and the Western Mediterranean area during the expansion/contraction of ice sheets related to DO cyclicity and AMOC changes; and 2) the palaeoclimate and palaeoenvironmental conditions during the scarcely known MIS 3, when the first Anatomically Modern Humans arrived on the Italian peninsula about 45.5 ka (Benazzi et al., 2011), sharing the territory with the already settled Neanderthals until the disappearance of the latter around 42 ka.

We present a well-dated continuous stalagmite record from Pozzo Cucù cave (southern Italy, Apulia) spanning from 106.0 ^+2.8/_-2.7 to 26.6 ^+0.8/_-0.9 ka, with an average uncertainty of less than 1 ka. The age model is based on 27 U-Th dates and about 2600 δ¹⁸O and δ¹³C analyses were performed at an average resolution of about 40 years. δ¹⁸O and δ¹³C are interpreted as rainfall and soil bioproductivity indicators, respectively, although moisture source possibly had a role in modulating δ¹⁸O. The δ¹⁸O-δ¹³C timeseries is the first western Mediterranean speleothem record duplicating the Greenland ice core record (NGRIP) for MIS 5 to 3, and showing a striking resemblance for most of the DO cycles, especially from DO 22 to DO 16 and from DO 11 to DO 4. Discrepancies exist too, especially during the early MIS 3. Interestingly, the speleothem does not show evidence of many of the most severe climate events affecting the northern latitudes (e.g. Heinrich events). This calls for a re-evaluation of the role of the northern high latitudes in triggering major cooling/drying events across the Mediterranean region.

The oldest remains of Anatomically Modern Humans in Europe were found in Apulia (about 45.5 ka), and Neanderthals are known to have existed there at least until 42 ka. Thus, our new record provides a palaeoclimate-palaeoenvironmental background for the arrival of Anatomically Modern Humans in southern Europe, their coexistence with the Neanderthals, and the disappearance of the latter, which marks one of the most important biocultural transitions in human history (Wolf et al., 2018).

References

Benazzi S et al., 2011. Early dispersal of modern humans in Europe and implications for Neanderthal behavior. Nature

Budsky A et al., 2019. Western Mediterranean climate response to Dansgaard/Oeschger Events: New Insights From Speleothem Records. GRL

Pérez-Mejías C et al., 2019. Orbital-to-millennial scale climate variability during Marine Isotope Stages 5 to 3 in northeast Iberia. QSR

Wolf D et al., 2018. Climate deteriorations and Neanderthal demise in interior Iberia. SR

How to cite: Columbu, A., Chiarini, V., Spötl, C., De Waele, J., Benazzi, S., Hellstrom, J., and Cheng, H.: A long continuous palaeoclimate-palaeoenvironmental record of the last glacial period from southern Italy and implications for the coexistence of Anatomically Modern Humans and Neanderthals, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-140, https://doi.org/10.5194/egusphere-egu2020-140, 2020.

In the area of the European-Asian border, in the Ural Mountains, the southern boundary of permafrost has moved in meridional direction by more than 1000 km in response to Quaternary climate variations. During cold climate states, permafrost extended as far south as the Southern Ural (53°N). We studied three independent archives in three caves in the Southern Ural (Shulgan-Tash, Victoria and Grandioznaya) in order to gain insights into the long-term dynamics of permafrost in the region.

Common speleothems (e.g., stalagmites and flowstone) require liquid water to form, and are therefore restricted to permafrost-free periods. Cryogenic cave carbonates (CCC) form when the temperature in the cave is close to or slightly below 0°C (permafrost conditions). These two types of speleothems were dated using the ²³⁰Th-U method in order to determine the timing of permafrost and permafrost-free conditions. As a novel indicator of freezing conditions in caves we identified frost wedges in silty cave sediments filled by sand. These sands were dated using OSL to constrain the timing of sub-zero rock temperatures (required to form frost wedges) in caves.

Stalagmites, abundant in in South Uralian caves, exhibit two prominent growth phases, associated with interglacials – MIS 5e and Holocene. In addition, mm-thin layers of flowstone formed in one chamber of Shulgan-Tash cave in association with smaller-scale warming episodes during MIS 3 (Greenland interstadials GI-9 and GI-8) and MIS 2 (GI-1; Bølling-Allerød). All CCC in Shulgan-Tash and Victora caves yielded MIS 3 ages, typically lagging cooling events (Greenland stadials) GS-16.1, GS-15.1, GS-13, GS-12, GS-10, and GS-7 by several hundred years up to one 1 ka. CCC from Grandioznaya cave formed during a single episode following GS-1 (Younger Dryas). Sand filling frost wedges in Victoria cave was washed into the cave during MIS 2, ca. 24-25 ka BP. Apparently, during this time the karst massif hosting the cave was engulfed by permafrost (to a depth of at least 90 m) and flow of water through the cave was severely restricted, which led to back-flooding of the cave passage and the accumulation of several m-thick silt deposits, interspersed with thin sand layers.

How to cite: Dublyansky, Y., Koltai, G., Scholz, D., Meyer, M., Gliganic, L., Kadebskaya, O., Cheng, H., and Spötl, C.: History of Late Pleistocene Permafrost in Southern Ural revealed by studies of speleothems and cave sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4800, https://doi.org/10.5194/egusphere-egu2020-4800, 2020.

Sedimentary sequences of the Dead Sea provide a unique high-resolution archive of past climatic changes in the Mediterranean-Levant, a key region for human migration out of Africa at the boundary of hemispheric climate belts. The well-preserved record of the Holocene Dead Sea and its Last Glacial precursor Lake Lisan is characterised by annual laminations – varves – composed of alternate layers of aragonite and detritus. Past lake level reconstructions suggest large fluctuations in the regional hydrological balance driven by abrupt climatic events, including a pronounced transition from lake level high-stand during the Last Glacial Maximum (LGM) to a low-stand at the onset of the Holocene [1]. On millennial timescales these changes have been associated with temperature variations recorded in the Greenland ice core, underscoring the potential of the Dead Sea to offer both regional and global perspectives on high-amplitude climatic events in the past. However, our ability to fully read the Dead Sea record critically depends on reliable extraction of palaeo-climatic and palaeo-environmental data from lacustrine carbonates, and an improved understanding of their formation. Here we present carbon, oxygen, boron isotope and trace element composition of hand-picked authigenic aragonite from a Dead Sea deep-drilling core (ICDP 5017-1; [2]) and shore outcrops. While traditionally used as a pH-proxy [3], we examine the possibility of applying boron geochemistry for reconstructing the source water and brine composition [4]. Using our innovative combined approach, we elucidate the palaeo-hydroclimatic evolution of the Dead Sea during intervals of major environmental changes since the end of the LGM.

[1] Torfstein A., et al. (2013) Quat. Sci. Rev. 69, 1–7.
[2] Neugebauer I., et al. (2014) Quat. Sci. Rev. 102, 149–165.
[3] Jurikova H., et al. (2019) Geochim. Cosmochim. Acta 248, 370–386.
[4] Vengosh A., et al. (1991) Geochim. Cosmochim. Acta 55, 1689–1695.

How to cite: Jurikova, H., Neugebauer, I., Plessen, B., Henehan, M., Tjallingii, R., Schwab, M. J., Brauer, A., and Blanchet, C.: Boron isotope systematics of lacustrine carbonates: a new approach for tracing the palaeo-hydroclimatic evolution of the Dead Sea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16623, https://doi.org/10.5194/egusphere-egu2020-16623, 2020.

Speleothems are powerful archives able to gain relevant paleoclimate information on temperature, moisture source or rainfall. Specifically, there is a need for new proxy related to past moisture availability, which would allow reconstruction especially in Europe, where such records are lacking. Among speleothem-based records, quantitative estimation of the water content (hereafter WC) remains rare as it is generally a collateral result of more challenging analyses such as isotope determinations of fluid inclusions or noble gases. Using a recently developed method to analyse speleothem fluid inclusion water isotopes (Affolter et al., 2014), we obtained a record of more than 250 WC data covering the Younger Dryas and Holocene intervals with a decadal to multi-decadal resolution measured on two Swiss stalagmites from Milandre Cave, NW Switzerland. The crushing of samples in the measuring line resulted in a mean WC of 1.9 microlitre of water per gram of crushed calcite from both stalagmites. The comparison with other paleohumidity-related indicators from central Europe suggests that the WC is related to past moisture variability. In addition, trace elements strontium (Sr) and magnesium (Mg) measurements as proxies for the water residence time and growth rate respectively are ongoing at the Department of Environmental Sciences at the University of Basel, which will further help with the interpretation of the WC. New reconstruction of past moisture variability together with speleothem fluid inclusion temperature estimates (Affolter et al., 2019) would allow a better understanding of the central European climate variability during the Holocene.

Affolter, S., Häuselmann, A., Fleitmann, D., Edwards, R. L., Cheng, H., and Leuenberger, M.: Central Europe temperature constrained by speleothem fluid inclusion water isotopes over the past 14,000 years, Sci Adv, 5, eaav3809, 10.1126/sciadv.aav3809, 2019.

Affolter, S., Fleitmann, D., and Leuenberger, M.: New online method for water isotope analysis of speleothem fluid inclusions using laser absorption spectroscopy (WS-CRDS), Clim Past, 10, 1291-1304, DOI 10.5194/cp-10-1291-2014, 2014.

How to cite: Affolter, S., Fleitmann, D., Häuselmann, A., and Leuenberger, M.: Speleothem water content as a proxy for past moisture variability in stalagmites from Milandre Cave, Switzerland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18849, https://doi.org/10.5194/egusphere-egu2020-18849, 2020.

Climate- and environmental-proxy time series obtained from different archives, such as speleothems, allowed for major leaps in the understanding of past climate and environmental dynamics. However, age uncertainties that arise from the applied dating techniques and from the proxy sampling methodologies, respectively, are often neglected. These age uncertainties are important when leads and lags between different proxy time series are examined or if the relationship to climate-forcing is investigated. This is most pronounced when examining data that detail events of sub-centennial down sub-annual resolution, where noise is not smoothed by a low resolution sampling (e.g. conventional dental drill), or in records karst systems where the noise is inherently high (e.g. water-limited environments).

We explore the use of dynamic time warping with a hierarchical aggregation layer (or HDTW) on multiple trajectories to generate an indexing table for the input samples. We hypothesize that this aggregation process results a temporally aligned references table (of the original trajectories) and allows for an analytical space to investigate and distinguish between local and non-local phenomena. We aim to compare sample derived features, such as peaks in trace element, organic fluorescence analyses and potentially δ¹⁸O (not tested here), on the derived analytical space, for the purpose of enabling a robust and simplified approach to multi-sample age modelling.

We show HDTW compatibility to existing peak-counting methodologies applied on laser-ablation trace element analysis and confocal fluoresce laser microscopy. As a case study, we use HDTW on three published micron-scale elemental measurements of samples from Mediterranean climates with strong dry summer – wet winter seasonality - two from south-western Australia (Nagra et al., 2017) and one from the Soreq Cave in the Eastern Mediterranean (Orland et al., 2014). The HDTW continuous space for these samples yields results that are within the published age constraints, without the need to stack multiple traverses and manually account for double or missing peaks.

HDTW is an important new tool for locating and identifying local and non-local phenomena in micron scale measurements (e.g. parallel laser ablation trace element traverses) by automatically aligning several coeval time axes of similar proxies. In the future HDTW could be applied for regional scale investigation (e.g. a coeval speleothems from a single cave or the same region, multiple cores from a single lake) allowing the unbiased fine-tuning between different environmental archives registering similar forcing mechanisms.

Nagra, G., Treble, P.C., Andersen, M.S., Bajo, P., Hellstrom, J.C., Baker, A., 2017. Dating stalagmites in Mediterranean climates using annual trace element cycles. Sci. Rep. 7, 621.

Orland, I.J., Burstyn, Y., Bar-Matthews, M., Kozdon, R., Ayalon, A., Matthews, A., Valley, J.W., 2014. Seasonal climate signals (1990–2008) in a modern Soreq Cave stalagmite as revealed by high-resolution geochemical analysis. Chem. Geol. 363, 322–333.

How to cite: Burstyn, Y. and Gazit, A.: Using hierarchical dynamic time warping to synchronize age-uncertain (proxy) time series, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1054, https://doi.org/10.5194/egusphere-egu2020-1054, 2020.

Stalagmites can provide long, accurate, and continuous palaeoenvironmental records of the Earth’s surface. However, insufficient or biased information on stalagmites has also been derived from some observed data, such as fluorescent annual-layer patterns and cave-climate monitoring data, which indicate sub-annual stalagmite growth rates can change with seasonal cave environments. Observations of stalagmite growth processes compared with cave-climate monitoring data provide an estimate of changes in growth rate. However, this method is considered unreliable as growth rates of normal stalagmites (~ 0.001 – 0.1 mm yr^-1) cannot provide sufficient data for validation. Many caves developed in uplifted Quaternary coral-limestones of subtropical islands in the Northeastern Pacific region.

The Gyokusen-do Cave in the southern part of Okinawa Island, southwest Japan, is famous for frequent and massive speleothems and as a tourist destination. This cave has stalagmites with a high growth rate (~ 1 mm yr^-1) along a pathway laid in 1987. The cave climate (temperature, carbon dioxide concentration, drop rates, and water chemistry) has been monitored since the summer of 2017. Distinctive seasonal changes in the cave environment are apparent in the data. In this study, we sampled sub-annual layer patterns collected in January 2019 from a stalagmite (~ 20 mm in length) on a stone wall in the cave and compared them with the cave-climate monitoring data and climate records near the study site, thus verifying the formation of annual layers. About 31 or 32 years are reflected in the (0.63 – 0.65 mm yr^-1) in the stalagmite record, because the stone wall was constructed in 1987. From base to top, the stalagmite has about 30 couplets of a transparent layer and a coarsely crystalline zone. The uppermost 5 mm has continuous layers without any hiatus, whereas concave points such as the drop position have thick layers of large crystals still in development. The stalagmite surface is covered with relatively large crystals that developed in the winter of 2018, which suggests that the winter climate produces coarse-grained layers precipitated during the winter season. The cave-climate monitoring data, collected about 150 m from the stalagmite, shows calcium ion concentrations of around 1 – 1.5 mol m^-3, temperature around 24 – 25 °C, and drastically different carbon dioxide concentrations in summer and winter seasons (around 400 – 500 ppm from the end of October to the beginning of May and around 2500 ppm from the middle of May to the middle of October). Precipitation and drop rates are highest in summer as compared to other seasons. Stalagmite growth simulations based on the monitoring data showed that the growth rate during the summer season was about five times that in winter. These results suggest that alternation between the transparent layer precipitated in summer and the coarse-grained layer precipitated in winter make annual layers that were strongly affected by drop rates and carbon dioxide concentrations. As some seasonal layers have significantly different thicknesses, more precise comparisons with cave-climate data are required to fully understand on the processes that occur in cave environments.

How to cite: Ishihara, Y., Ooka, S., Sasaki, H., and Yoshimura, K.: Comparison of annual-layer formation pattern and climate monitoring data: an example of a stalagmite from Gyokusen-do Cave, Okinawa Island, southwest Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2536, https://doi.org/10.5194/egusphere-egu2020-2536, 2020.

Several caves have been monitored along a transect stretching from the Adriatic Sea to the Aggtelek Karst (NE-Hungary) including two caves in Croatia and three caves in Hungary:  1) Cerovacke cave (~25 km far from the sea, Velebit Mt.), 2) Baraceve cave (~70 km far from the sea), 3) Csodabogyós Cave (~320 km far from the sea, Keszthely Mt.), 4) Béke and Baradla Caves (~700 km far from the sea, Aggtelek Karst). The monitoring activities in each caves included microclimate measurements, analyses of the elemental and stable isotope compositions of drip water and precipitation, as well as stable isotope measurements of modern calcite precipitates formed on light bulbs or glass plates.

The stable isotope compositions of the drip waters in all cases (except one) show systematically lower values than those found in amount-weighted annual precipitation suggesting that the source of the infiltrating water dominantly derives from winter precipitation. Moreover, the relative contribution of winter precipitation can vary even within same cave system reflecting also the local morphology of the karst above the cave. The d-excess values of the drip waters show an increasing trend from the Aggtelek Karst towards to Adriatic Sea, showing higher values than 10‰ (Béke-C.: 10.3‰; Csodabogyós-C.: 11‰, Baraceve-C.: 12‰, Cerovacke: 15‰). These observations indicate significant contribution from moisture originated from the Mediterranean Basin to the infiltrating water. The monitoring of the precipitation support these findings as among the marine moisture source the Mediterranean is the most dominant even relative far from the sea.

The trace element systematics in drip waters indicate that PCP likely took place during relatively dry periods. In some caves the change of the hydrological condition affected both the trace element composition of the drip water and the stable isotope composition of the modern calcite precipitates. Although the calcite-water isotope fractionations show significant scatter even within individual caves, the majority of the data fall close to the Coplen (2007) and the Tremaine et al. (2011) fractionation values in both Croatian and Hungarian caves.

The research was supported by the Ministry for Innovation and Technology, the National Research, Development and Innovation Office (project No. PD 121387).

How to cite: Czuppon, G., Demény, A., Bocic, N., Buzjak, N., Kármán, K., Kovács, Z., Leél-Össy, S., John, S., Óvári, M., and Bottyán, E.: Monitoring activities in several caves along a transect stretching from the Adriatic Sea to the Aggtelek Karst (NE-Hungary): trace element and stable isotopic compositions of drip waters and cave carbonates, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11089, https://doi.org/10.5194/egusphere-egu2020-11089, 2020.

We present a high-precision record of the Penultimate Interglacial (MIS 7) and the Penultimate Glacial inception (MIS 7–6 transition) from Spannagel Cave in the central European Alps (southern Austria). Drip waters in this high-elevation cave are largely sourced from the overlying low-permeability gneiss, giving rise to unusually high uranium concentrations in secondary calcite deposits (up to 200 ppm). The large quantities of ²³⁴U and ²³⁰Th incorporated in samples can be measured using high-precision spectrometry, resulting in relative age uncertainties as low as 1‰ (2σ) during our study period (~250 to 197 thousand years ago [ka]). Using this unprecedented age control, we revisit Spannagel stalagmite SPA121 that grew continuously throughout MIS 7 and the MIS 7–6 transition. Previous work by Spötl et al. (EPSL 2008) revealed that SPA 121 δ¹⁸O displays similar timing and structure to global benthic marine δ¹⁸O during MIS 7, including distinct sub-stages. New dating allows us to constrain the exact timing and duration of MIS 7 sub-stages in the European Alps, including the timing of Terminations (T) III and IIIa. Preliminary results show the onset of MIS 7e at 241.4 ± 0.3 ka, the δ¹⁸O minima during MIS 7b at 224.5 ± 0.3 ka, and the mid point of TIIIa at ~216.2 ± 0.3 ka. The onset of decreasing δ¹⁸O associated with the MIS 7a–6e transition occurred no later than 193.0 ± 0.2 ka. Two newly collected stalagmites from this cave (SPA146 & 183) provide two high-resolution replications of the MIS 7a–6e transition. The resulting multi-stalagmite record will provide important chronological constraints on climate shifts in the European Alps during the Penultimate Interglacial and subsequent glacial inception.

How to cite: Wendt, K., Li, X., Cheng, H., Edwards, R. L., and Spötl, C.: High-precision dating of MIS 7 using Austrian Alp stalagmites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18124, https://doi.org/10.5194/egusphere-egu2020-18124, 2020.

Fluorescent annual layers with thicknesses of 0.01–0.1 mm occur frequently in stalagmites around the world. Aggradational variations of fluorescence intensity expressing those annual layers have been postulated as being caused by seasonal fluctuations of the supply of fulvic acid from the surface. The variation patterns of fluorescence intensity in annual layers can be classified into symmetric, gradually increasing, and gradually decreasing types. Numerical simulation of fluorescent annual-layer patterns based on the stalagmite-formation model suggests that various patterns of fluorescence intensity in annual layers can form by time lags between a growth season and the fulvic acid supply peak on a stalagmite. However, verification of those fluorescence patterns requires long-term cave climate monitoringin caves. In this study, we simulated fluorescence intensity variations in a modeled stalagmite based on cave climate monitoring data from a cave in a humid-temperature climate and validated annual layer formations.

Cave climate monitoring was performed at point A (40 m inside the entrance), point B (90 m inside the entrance), and other points in Koumori-ana Cave, Mine City, Yamaguchi Prefecture, southwest Japan, from the end of 2016. The monitoring data included cave air temperatures, CO₂ concentrations, and drip rates. Ca²⁺ concentrations and relative fluorescence intensities to quantify fulvic-acid concentrations were measured monthly from drip-water samples.

The monitoring data showed that cave temperatures decrease in winter near the entrance and increase in summer near the upper vent. Drip rates at point A corresponded to rainfall amounts at the meteorological station in Akiyoshi-dai, whereas drip rates at point B were constant throughout the years monitored. CO₂ concentrations in the cave, closed to outside air values from November to March, became greater from April and reached maximum values in September. Ca²⁺ concentration had gradual seasonal variations, showing a maximum in October and a minimum in March. The relative fluorescence intensities, showing fulvic acid concentration, at both points revealed a change range of about four times the minimum.

The stalagmite-growth simulations based on the monitoring data showed different growth patterns at the two monitored points: continuous growth at one and hiatus at the other. The calculated fluorescent annual layer at point A was the symmetric or gradually increasing type, with high concentration of fulvic acid in August. The growth rate varied in the range of 0.45 (Jan–Apr) to 6.2 (May–Oct) µm/month. Because the relative fluorescence intensity of fulvic acid had small variations throughout the years, the simulated fluorescent annual layer at point A is suggested to be affected by the growth rate of stalagmite. At point B, decreased saturation indices of calcite from April to June and September to October suggest no precipitation of calcite. Although the simulated annual thickness of precipitation at point B is around 28 µm, half of the thickness is precipitated in July. Point B stalagmite growth is stopped by a high concentration of CO₂, low Ca²⁺ concentration, and low drip rate. This study suggests that specific seasonal paleoenvironmental changes recorded in stalagmites can be estimated by using fluorescence patterns of annual layers.

How to cite: Sasaki, H., Onishi, Y., Ishihara, Y., Murakami, T., and Yoshimura, K.: Simulation of fluorescent annual-layer patterns in stalagmites based on cave climate monitoring data: an example from Komori-ana Cave, Akiyoshi-dai Plateau, southwest Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2575, https://doi.org/10.5194/egusphere-egu2020-2575, 2020.

The last deglaciation was a period of rapid and profound climatic change in Western Europe. Speleothem carbon isotope (δ¹³C) records from mid-latitude Western Europe have consistently shown large and reproducible excursions over this time period, strikingly similar to available temperature reconstructions from other archives. The mechanism behind the temperature sensitivity of speleothem δ¹³C, however, remains poorly constrained, due to the complex interplay of multiple processes affecting this proxy.

Here we use a multi-proxy approach and forward modelling of karst processes to investigate what drives the response of speleothem δ¹³C to the last deglaciation in Western Europe. We present new proxy data (¹⁴C and δ⁴⁴Ca) from speleothem Candela from El Pindal Cave, northern Spain, which covers the period from the Last Glacial Maximum (25 ka BP) to the Early Holocene (8 ka BP). Previously published stable isotope data (Moreno et al., 2010) revealed a pronounced decrease in δ¹³C over the deglaciation (~8‰ VPDB) which closely tracks regional temperature records from the Iberian Margin. We make use of the different sensitivities of ancillary proxies (¹⁴C, Mg/Ca, and δ⁴⁴Ca) to processes in soil and karst to quantify their relative importance on the δ¹³C shift. For this, we use the forward modelling software CaveCalc (Owen et al., 2018) to generate a large ensemble of possible solutions, from which the ones closest matching the data are chosen and evaluated.

Our preliminary results suggest that in-cave and karst processes (carbonate host rock dissolution and reprecipitation) cannot explain the full amplitude of the δ¹³C shift over the deglaciation, and that changes in soil δ¹³C are to some extent translated to the speleothem carbonate δ¹³C. The possibility of quantitatively disentangling processes in the soil from other karst processes could allow the reconstruction of past soil activity from speleothems.

References:

Moreno, A., Stoll, H., Jiménez-Sánchez, M., Cacho, I., Valero-Garcés, B., Ito, E., Edwards, R.L., 2010. A speleothem record of glacial (25-11.6 kyr BP) rapid climatic changes from northern Iberian Peninsula. Glob. Planet. Change 71, 218–231. doi:10.1016/j.gloplacha.2009.10.002

Owen, R.A., Day, C.C., Henderson, G.M., 2018. CaveCalc: A new model for speleothem chemistry & isotopes. Comput. Geosci. doi:10.1016/J.CAGEO.2018.06.011

How to cite: Lechleitner, F. A., Day, C. C., Wilhelm, M., Haghipour, N., Kost, O., Henderson, G. M., and Stoll, H. M.: Understanding the deglacial relationship between carbon isotopes and temperature in stalagmites from Western Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7466, https://doi.org/10.5194/egusphere-egu2020-7466, 2020.

The Arctic region is predicted to be one of the most sensitive areas of the world to future anthropogenically-forced climate change, the consequences of which will affect vast numbers of people worldwide, for instance through changes to mid-latitude weather systems and rising eustatic sea levels. Recent changes in temperature and precipitation, and those projected for the future, indicate that some of the greatest changes will occur in Northeast Greenland. Essential knowledge on the climate history of this region, which can be used to validate models and understand forcing mechanisms and teleconnections, is however absent. Here, we present a speleothem palaeoclimate record for Northeast Greenland (80 °N) that formed during Marine Isotopes Stage 15a  between 588 ka to 537 ka. The record indicates that at that time, Northeast Greenland was warmer and wetter than at present associated with a reduction in Arctic sea ice, thawing of permafrost in eastern Siberia (55 °N and 60 °N), and elevated warm conditions at Lake El’gygytgyn (67.5 °N), Russia.

How to cite: Moseley, G., Edwards, R. L., Spötl, C., and Cheng, H.: Speleothem record of enhanced hydroclimate during MIS15a in Northeast Greenland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22391, https://doi.org/10.5194/egusphere-egu2020-22391, 2020.

North Africa is a key region to study the interactions between low-latitude African monsoon systems and high-latitude millennial-scale climate change. Here, we present new high‐resolution δ¹⁸O records and preliminary Δ¹⁷O data (deviation of triple oxygen isotope data between δ¹⁷O and δ¹⁸O) from four Southwest Moroccan speleothems (⁓31°N) spanning the last glacial period. Our δ¹⁸O records provide evidence of humid conditions during the Marine Isotope Stage (MIS) 5 and the early to mid‐Holocene. The apparent increase in moisture during these Green Sahara periods is linked to the increase of summer insolation and the resulting expansion of the West African monsoon fringe, which could reach 31°N in NW Africa. Furthermore, the preliminary Δ¹⁷O results support our interpretation of δ¹⁸O data and reveal substantial changes in moisture sources and climate regimes between glacial and interglacial cycles.

Additionally, the Green Sahara periods are good examples to illustrate how dramatic climate change could shape human life in Africa – the original home of anatomically modern humans (AMH). Archaeological evidence shows that the human populations in North Africa during MIS5 were geographically well placed to disperse after the “Green Sahara” faded. Our climate record shows an abrupt deterioration of climate conditions during the MIS5-MIS4 transition, which has been proposed as one of the main factors that pushed AMH to move into Eurasia. Interestingly, the MIS5-MIS4 transition is characterized by a decrease of summer insolation and the occurrence of the Heinrich events 7a and 7b, which possibly induced a southern shift of the Intertropical Convergence Zone (ITCZ) and, therefore, a retreat of the African monsoon during this period.

How to cite: Ait Brahim, Y., Sha, L., Wassenburg, J. A., Cruz, F. W., and Cheng, H.: Green Sahara periods and climate-human interactions during the Last Glacial Period: Evidence from Northwest African speleothems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13062, https://doi.org/10.5194/egusphere-egu2020-13062, 2020.

The Last Interglacial (LIG, ~130–116 ka) was one of the warmest interglacials of the past 800,000 years. Although the orbital configuration was different, the LIG is a useful test bed for the future of the Holocene, because LIG archives have a higher preservation potential and can be dated at much higher precision than older interglacials, e.g. Marine Isotope Stage 11. Speleothems are among the most important terrestrial archives to study the climate of the LIG. Only few well-dated such studies, however, have been published for Europe and there are significant uncertainties regarding the timing of the onset and the magnitude of the peak warmth between some of these reconstructions.

The European Alps have shown to be a climatically highly sensitive region with a warming trend twice the average of the Northern Hemisphere. We therefore examined Alpine caves and studied stalagmite records of the LIG to gain insights into how this mountain range was affected by a warmer climate than today. We present a new, replicated and precisely dated speleothem stable isotope stack from two caves in the Western Alps and two caves in the southeastern Alps. Modern and paleodata show that the O isotopic composition of meteoric precipitation is a function of the mean air temperature in most parts of the Alps. Western stalagmites record an initial warming at 129.6 ± 0.4 ka and reach a first O isotope plateau at 129.0 ± 0.4 ka. An early optimum is identified after the first warming until 127.4 ± 0.5 ka, followed by a cooling until 126.6 ± 0.5 ka. The warming continued but the growth rate slowed down from 126.2 ±0.4 ka to 123.7 ±0.8 ka. Toward the end of the record (123.7 ±0.8 ka) the carbon isotopes slightly rise toward less negative values, possibly indicating climate cooling. The southeastern Alpine stalagmites started growing after Termination II (between 129.1±1.1 ka and 128.5±0.5 ka) and the oxygen isotope values slightly increase from 129 to 120 ka. At the onset of the LIG the carbon isotope values show a stepwise decrease as the oxygen isotope values become less negative, documenting the expansion of vegetation and the gradual soil development during the early part of the LIG. Vegetation and soil bioproductivity peaked around 126 ka in the west and at 125 ka in the southeast. Growth in the west was interrupted soon after 125 ka while in the southeast the carbon isotope signal stayed stable until 123 ka. The final decrease in vegetation density towards the end of the LIG was less synchronous among the southeastern speleothems and was characterized by abrupt shifts. Most stalagmites stopped growing after 119 ka when the carbon isotope values reached their highest values indicating a decrease in soil activity and/or vegetation density, possibly associated with deforestation. 

How to cite: Honiat, C., Spötl, C., Jaillet, S., Wilcox, P., Racine, T., Edwards, R. L., and Cheng, H.: Last interglacial speleothem records from the western and southeastern side of the Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19466, https://doi.org/10.5194/egusphere-egu2020-19466, 2020.

We investigated the uranium isotope systematics in an alpine cave environment (central Switzerland). We measured the U concentration and the ²³⁴U/²³⁸U activity ratio of the two main host rock formations in which the cave developed and the ²³⁴U/²³⁸U activity ratio of drip water. We further investigated the U characteristics of young carbonate precipitates (< 500 a old) at these drip sites. In addition, we analysed several speleothems between 1 and ~200 ka old. We observe variable U concentrations (between 0.1 – 5 ppm) and a significant spread in the initial activity ratio of ²³⁴U/²³⁸U (between ~1 and 5) between individual drips and individual stalagmites. In general, high U concentrations are accompanied by low initial ²³⁴U/²³⁸U ratios and vice versa. However, these data do not follow a binary mixing line between the two host rock endmembers (both show low U concentrations of about 1 ppm). Instead, we argue that redox processes within the karst might govern the U systematics of cave drip water and speleothems, as high and variable SO4^2- concentrations in drip water are observed, which point to at least locally constrained anoxic conditions in the host rock. The dependence of the initial ²³⁴U/²³⁸U activity ratio and U concentration of the stalagmites from this cave in concert with the partly large absolute value in their initial activity ratio open the perspective for dating speleothems from this karst region back to ~1 Ma.

How to cite: Schröder-Ritzrau, A., Fohlmeister, J., Trüssel, M., Förstel, J., Frank, N., Spötl, C., and Luetscher, M.: Uranium isotope systematics in the Melchsee-Frutt cave region (Central Swiss Alps), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6972, https://doi.org/10.5194/egusphere-egu2020-6972, 2020.

The climatic controls of stalagmite radiocarbon (¹⁴C) remain one focus of modern paleoclimatology due to recent efforts and achievements in ¹⁴C calibration. The Hulu cave ¹⁴C record (Cheng et al., 2018) has proven the potential of stalagmites from temperate climate zones for atmospheric ¹⁴C reconstruction. However, a constant dead carbon fraction (DCF) in stalagmites over long periods is rather exceptional. In our study, a high-resolution ¹⁴C record (N=111) of a precisely U-Series dated stalagmite from Sofular Cave (Northern Turkey) with elemental Mg/Ca ratio data is presented. A phase of low and constant DCF (12.5% ± 1.6%, N=20) between 10 and 14 kyr BP, together with relatively stable Mg/Ca ratios suggest stable hydrological soil/karst conditions above the cave. However, we observe unstable soil conditions for the period before 14 kyr BP where DCF is strongly variable between a lower threshold of approximately 5% and an upper limit of 25%. Near a phase of slow growth at ~17 kyr BP DCF as high as 38% is observed on sub-centennial timescales.  The combination of stable isotopes, element ratios, radiocarbon and U-series data allows for multi-proxy analysis of the impact of rapid climate changes like D/O events on the incorporation of ¹⁴C into stalagmites. Between 15 and 27 kyr BP, hydrological changes have a large impact on limestone dissolution systematics which is reflected in fast DCF variations on sub-centennial timescales. A growth stop between 21 and 23 kyr BP is resolved. Although a comprehensive reconstruction of atmospheric ¹⁴C variations is not possible for the entire growth period, the stalagmite reproduces the deviation from the IntCal13 record (Reimer et al. 2013) seen in the Hulu ¹⁴C data at ~40 kyr BP during the Laschamp geomagnetic reversal and provides further inside on the climate dependency of ¹⁴C incorporation in stalagmites.

References

Cheng, H., Lawrence Edwards, R., Southon, J., et al.: Atmospheric ¹⁴C/¹²C changes during the last glacial period from Hulu cave, Science, 362(6420), 1293–1297, doi:10.1126/science.aau0747, 2018.

Reimer, P. J., Bard, E., Bayliss, A., et al.: IntCal13 and Marine13 Radiocarbon Age Calibration Curves 0–50,000 Years cal BP, Radiocarbon, 55(4), 1869–1887, doi:10.2458/azu_js_rc.55.16947, 2013.

How to cite: Therre, S., Fohlmeister, J., Fleitmann, D., Friedrich, R., Lausecker, M., Schröder-Ritzrau, A., and Frank, N.: Atmospheric and Soil Signals in a Climate Dependent Stalagmite Radiocarbon Record from Northern Turkey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17760, https://doi.org/10.5194/egusphere-egu2020-17760, 2020.

The eastern part of Romania, bordering on the Black Sea, is generally poor in speleothems and only Piatra Cave has important speleothem occurrences. This cave is positioned close to the present-day shoreline, forcing the local aquifer to completely flood it when it rose synchronously with sea level. The flooding of the cave prevented speleothem formation. Conversely, sub-aerial carbonate deposition took place when the sea level was lower than today and the cave was dry. The study of speleothems from Piatra Cave could bring more insight on past Black Sea level fluctuations, as well as on the isotopic composition of percolating water.

Some 50 km to the south of Piatra Cave, around the town of Mangalia, botryoidal calcite has been deposited inside small voids formed between Sarmatian limestone beds. Such calcite formations are considered to form close to the water table, at the contact with the underground atmosphere. If so, they could be used to track the position of past water tables, as well as the isotopic composition of those waters. Moreover, as these samples are found only close to the present-day shoreline, they might have been deposited from underground water whose level was directly controlled by the sea.

Here we present the results of δ¹⁸O and δ¹³C measurements on 75 samples and sub-samples of botryoidal calcite. We explore the implications of their isotopic variability, by comparison with speleothems from Piatra Cave as well as to other speleothems from Romania. Moreover, we explore their isotopic variability across the sampling area, in order to better assess their possible use as sea level markers.

How to cite: Dragusin, V., Constantin, S., Ersek, V., Hoffmann, D. L., and Hotchkies, A.: Pleistocene carbonates from Dobrogea (E Romania) and their relationship with Black Sea level fluctuations , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10485, https://doi.org/10.5194/egusphere-egu2020-10485, 2020.

The dynamic interaction between synoptic systems across the Iranian Plateau in West Asia has made this region highly sensitive to climate change.   Early human migration routes in the region from Africa to Eurasia are marked by Paleolithic sites and provide a unique opportunity to study the impact of climate variability on early human mobility and settlement. Preliminary results are based on δ¹⁸O and elemental time series from three stalagmites in central-northwest Iran with robust U-Th chronology over the last 450,00 years The data raise the possibility that the Iranian Plateau experienced several episodes of wet conditions during the Paleolithic period. This is in line with findings from a compilation of independent proxy records of lake sediment in northwest Iran and loess deposits in northeast Iran. The fluctuation of Mn abundance and δ¹⁸O values in these stalagmites correlate with the Greenland ice core record (NGRIP) and coincide with periods of high solar intensity in the northern hemisphere. These early results indicate wet conditions may have prevailed over the Iranian Plateau during marine isotope stages MIS5a,b, MIS5c, MIS5e, MIS6b, MIS6d-e and most likely also during stages MIS3-4 and MIS7a. Early human occupation of the Southern Caucasus, Zagros, and the Near East regions coincides with the upper Pleistocene wet periods. The co-variability between the proxy data from these speleothems and solar insolation at 30°N suggests that early human settlements/occupations may have been more prevalent along coastal regions of the Near East during dry climate episodes.

How to cite: Sharifi, A., Pourmand, A., Sevag, M., Swart, P., Peterson, L., and A. K. Lahijani, H.: Climate driven mobility of the early humans in SW Asia: Preliminary evidence from Iranian Stalagmites, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19608, https://doi.org/10.5194/egusphere-egu2020-19608, 2020.

During the Terminal Classic Period (c.800-1000CE) most major Maya centres in the lowlands of the southern Yucatán Peninsula declined and were then abandoned, in what would come to be known as the Classic Maya Collapse. The causes of this societal transformation remain open for debate in modern archaeology. Over the past 25 years, palaeoclimatic records from lake sediments and speleothems have prompted discussion about the role abrupt climate change may have played in the decline. These records largely indicate the existence of a Terminal Classic Drought, a period of increased drought frequency that is approximately contemporaneous with the Collapse.

The high temporal resolution of speleothem archives makes them an important tool in assessing the validity of these records. Previous work has demonstrated the prevalence of drought in the lowlands of both northern and southern Yucatán during the Terminal Classic and Early Postclassic Periods. However, it has been difficult to build a detailed understanding of regional rainfall changes owing to the large spatial and temporal variability of precipitation over the Peninsula, as observed in the modern day.

Here we report a high-resolution (100µm), absolutely-dated, replicated record of δ¹⁸O and δ¹³C variations in two stalagmites from Columnas Cave (Rancho Hobonil) near the Puuc Hills, a dominant region of Maya settlement in north-western Yucatán during the Terminal Classic. The oxygen and carbon isotopic records of the speleothems (designated Hobo-5 and Hobo-6), located <10m apart in the farthest reaches of the cave, can be correlated with one another in great detail. The highest δ¹⁸O values in both speleothems occur during the Terminal Classic Period, coupled with the onset of an extended period of consistently high δ¹³C values. These are interpreted as representing a period of increased drought frequency; as documented from sediment cores in nearby Lake Chichancanab, located ≈30km from Columnas Cave. These replicated records provide strong evidence for highly variable climatic conditions in the Terminal Classic, when the Puuc Maya underwent several boom-bust cycles. Ultrahigh-resolution (10µm) SIMS isotope and synchrotron µXRF analyses during this critical period have been undertaken to test if an annual record of climatic changes can be developed.

Radiocarbon data across the Terminal Classic also displays a single abrupt increase in 14C content around 1000CE, indicating a decrease in the dead carbon fraction. This event occurs close in time to the 994CE solar proton event documented in tree rings. If these events are indeed synchronous, it would constitute the first instance of the cosmogenic radiocarbon event being recorded in a speleothem, which would provide a valuable absolute correlation horizon.

How to cite: James, D., Breitenbach, S., Cheng, H., Hartland, A., Orland, I., Brenner, M., Curtis, J., Gallup, C., Szidat, S., Nicolson, J., Rolfe, J., Mason, A., Henderson, G., and Hodell, D.: The Maya Terminal Classic Drought replicated in two stalagmites from Columnas Cave, NW Yucatán, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18326, https://doi.org/10.5194/egusphere-egu2020-18326, 2020.

Hydroclimatic variability over the Volga River watershed (western Russia) strongly influences agricultural production, forest and grassland ecology, Caspian Sea level, and associated economic stability. Climate model forecasts of these variables suggest long-term increases in crop shortfalls and over-basin evaporation in the Volga and Caspian regions, respectively, but these projections currently lack validation from high-quality paleoclimate data. We present decadal-scale geochemical proxy data (δ¹³C, Mg/Ca, Sr/Ca) from ²³⁰Th-dated stalagmites retrieved from four caves along a 640-km north-south gradient in the Ural Mountains, which collectively cover the entire Holocene (11.7 ka to present). Orbital trends in δ¹³C and Mg/Ca are broadly coherent between Ural speleothems and suggest that following Early Holocene aridity, warm-season precipitation was paced by summer insolation and has gradually declined since ~8 ka, consistent with model hindcasting. Centennial-scale variability, which is exceptionally well replicated between the Southern (Kinderlinskaya Cave) and Central (Geologov-3 Cave) Ural sites, supports a dynamic link between Volga hydroclimate and sea-surface temperature in the northeastern North Atlantic and Barents Sea. Important discrepancies exist, however, with data from the southernmost cave sites, which may be related to past migration of a strong latitudinal precipitation gradient that characterizes the modern basin and approximates the limit of North Atlantic influence. Finally, we conduct model-data comparisons and review our composite dataset in light of pollen- and soil-based proxies from across the Volga region, as well as reconstructions of Caspian Sea level. Our results provide a temporally well-constrained and spatially coherent portrait of Holocene hydroclimate for the Volga River watershed, thus constituting an important metric for future modeling studies.

How to cite: Baker, J., Dublyansky, Y., Kadebskaya, O., Scholz, D., Koltai, G., Li, H., Zhao, J., Spötl, C., and Cheng, H.: Holocene hydroclimate of the Volga Basin recorded in speleothems from the Central and Southern Ural Mountains, Russia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10343, https://doi.org/10.5194/egusphere-egu2020-10343, 2020.